The prior art includes many rotary pumps for pumping liquids such as water, oil, gasoline, and other materials. In such pumps, the tolerance of clearance between the impellers and the pump chamber is critical to the proper functioning of the pump. The clearance must be great enough so the impellers do not touch a pump chamber wall and destroy various components of the pump, yet small enough that the pump operates efficiently and with minimal vibration by pushing the liquid through the pump chamber. Moreover, such pumps must be made out of materials that can maintain the required critical tolerance and withstand extreme vibration. As such, rotary pumps are expensive to manufacture and may suffer from a lack of a high degree of tolerance. Furthermore, many rotary pumps are difficult and expensive to maintain since after excessive wear, the entire impeller needs to be replaced.
U.S. Pat. No. 1,348,772 to Auger teaches the use of packing material, such as felt, on a end of each lobe of a rotary pump to help increase the efficiency of the pump. However, packing materials wear out quickly which reduces efficiency of the pump unless the packing material is replaced frequently. Additionally, materials such as felt are semi-porous which allows flow though the material and reduces efficiency. Furthermore, the packing material may come loose from the lobe at high speeds as the pump impellers rotate, which greatly reduces the efficiency of the pump, rendering it unusable.
An impeller lobe is most efficient when in extremely close proximity with either a housing or another impeller. Without a small tolerance between the impeller lobe and either the housing or other impeller, excessive backflow occurs resulting in lower efficiency. Additionally, the interaction between the area where the surface of one lobe tip comes in close proximity with the other impeller can cause hydraulic hammering which causes vibration and unnecessary wear of the shaft bearings. A general need is recognized to reduce the space between the lobe tip and either the housing or other impeller while limiting vibration and damage to the pump.
Therefore, there is a need for a rotary pump having a high degree of tolerance which is inexpensive to manufacture, maintains contact with either the interior chamber wall or other impeller, has an increased-wear replaceable wiper blade which does not come loose at high speeds, and which can be changed quickly and efficiently without significant expense.